A differential absorption lidar (DIAL) has been developed at LMD to measure the variation of stable isotopic composition of CO2, δ 13C, in the atmosphere. The lidar uses a new 3-wavelengths single mode hybrid fiber/bulk pulsed laser at 2 µm and a coherent detection. We present the geophysical objectives of this work, the expected performances and the experimental set-up. Preliminary atmospheric results will be discussed at the conference.

A differential absorption lidar (DIAL) based on an Er:YAG laser was used to retrieve methane concentration profiles within the mixed layer along a near-horizontal line of sight (4° above the horizontal) from the École Polytechnique site, directed northward toward the western part of the city of Paris. The achieved precision remains below 1 % up to a range of 3.5 km for profiles with a spatio-temporal resolution of 470 m per 20 min. The measurements were compared with in situ observations from an ICOS (Integrated Carbon Observation System) site located 5 km from the lidar. The lidar successfully captured the late stage of the dispersion of a methane plume originating from a fire occurred at a waste-sorting facility in the city of Paris, in good agreement with the in situ measurements. Both random and systematic errors in the lidar measurements are dominated by uncertainties in the ON wavelength measurement.

Our understanding of the global carbon cycle needs for new observations of CO2 concentration at different space and time scales but also would benefit from observations of additional tracers of intra-atmospheric or surface-atmosphere exchanges to characterize sources and sinks. Lidar is a well-known promising technology for this research as it can provide, at the same time, structure of the atmosphere, dynamics and composition of several trace gas concentration. In this framework, a coherent differential absorption lidar (CDIAL) has been developed at LMD to measure simultaneously and separately 12CO2 and 13CO2 isotopic composition of CO2 in the atmosphere. It also provides the radial wind speed along the line of sight of the laser. This paper investigates the methodology of three wavelengths DIAL in the spectral domain of 2 & micro;m to obtain range-resolved CO2 isotopic ratio delta 13C. The set-up of the lidar as well as the signal processing is described in details. First atmospheric measurements along three days are achieved in the surface layer above the suburban area of Ecole Polytechnique campus, Palaiseau, France. Typical performances of the instrument (median values along 70 h of measurement) with 10 min of time averaging show: (1) a precision around 0.6 % for 1.2 km range resolution for 12CO2 mixing ratio (2) a precision around 3.2 % for 1.6 km range resolution for 13CO2 mixing ratio. In situ co-located gas analyser measurements are used to correct for biases that are explained neither by the spectroscopic database accuracy nor the signal processing and will need further investigation. Nevertheless, this preliminary study enables to make a useful state of the art for current lidar ability to provide delta 13C measurements in the atmosphere with respect to geophysical expected anomalies and to predict the necessary performances of a future optimized instrument.

MERLIN (MEthane Remote LIdar missioN) is a space mission developed by France and Germany to monitor the atmospheric methane using an IPDA (Integrated Path Differential Absorption) lidar. The mission is scheduled for launch at the end of the decade. Currently, the LMD (Laboratoire de Météorologie Dynamique) is working on improving spectroscopy data, end-to-end modelling of the instrument to study the sensitivity of measurements to different sources of uncertainty, developing an inversion system to study the impact of certain data processing parameters, setting up measurement campaigns to better understand methane variability and fluxes, as well as developing a ground-based differential absorption lidar for CH 4 profiling.

A differential absorption lidar (DIAL) has been developed at LMD to measure the variation of stable isotopic composition of CO 2 , δ 13 C , in the atmosphere. The lidar uses a new 3-wavelengths single mode hybrid fiber/bulk pulsed laser at 2 µm and a coherent detection. We present the geophysical objectives of this work, the expected performances and the experimental set-up. Preliminary atmospheric results will be discussed at the conference.

Abstract. Understanding the global carbon cycle requires observation of carbon diffusivity within the convective boundary layer (CBL). In particular, observations of the vertical evolution of CO2 turbulent flux would enable the evaluation of the spatial representativeness of in situ flux measurements and the quantification of entrainment-flux impacts on such measurements. Coherent lidar is a promising technology for this purpose, as it can perform ground-based range-resolved measurements of CO2 mixing ratio and vertical wind speed along the height of the CBL. Still, achieving a sufficiently low statistical error in the CO2 mixing ratio measurement is a key challenge in CO2 turbulent flux measurements. For this purpose, a 2.05 µm coherent differential absorption lidar (CDIAL) has been developed. This lidar features a hybrid fiber/bulk amplification chain that provides 20 kHz high pulse repetition frequency and 1 mJ pulse energy. These characteristics allow for a random error of about 30 ppm in CO2 mixing ratio measurements and 0.01 m s-1 in wind velocity, with a spatiotemporal resolution of 13 s and 115 m, enabling turbulent flux measurements. This paper presents a performance assessment of CO2 turbulent flux measurements with this CDIAL lidar, under typical meteorological conditions of CO2 uptake by photosynthesis. A new expression for random error after spatial averaging is introduced, that is verified using Monte Carlo simulations and statistical analysis on experimental measurements. CO2 fluxes measured by the lidar are discussed with respect to flux measurements made by in situ instruments. The lidar enables flux measurements over the convective boundary layer height (around 1000 m), and achieves a minimum flux detection limit of 11 µmol m-2 s-1 at a spatiotemporal resolution of 350 m and 4 hours, making it well suited for future geophysical studies of CO2 turbulent fluxes.

We report on the development of a DIfferential Absorption Lidar (DIAL) with coherent detection using a hybrid fiber/bulk laser for CO2 and wind measurement at 2.05 µm. Peak power is limited at 0.6 kW by Stimulated Brillouin Scattering in the fibered part. A Ho:YLF bulk amplifier allows to overcome this limitation, providing 12-19 dB additional gain depending on the pulse repetition frequency. The hybrid fiber/bulk architecture delivers laser pulses of 1.5 mJ, 200 ns at 20 kHz (30 W average power). The architecture provides easy tunability on pulse repetition frequency, duration, and wavelength emission around the absorption line. This flexibility allows for the adjustment of the compromise between measurement range and precision. Firsts measurements of CO2 Volume Mixing Ratio (VMR) and wind speed are currently being carried out. Then, the system will be used to measure CO2 emissions from thermal plants and atmospheric CO2 fluxes using eddy covariance calculations.

MERLIN (MEthane Remote LIdar missioN) is a space mission developed by France and Germany to monitor the atmospheric methane using an IPDA (Integrated Path Differential Absorption) lidar. The mission is scheduled for launch at the end of the decade. Currently, the LMD (Laboratoire de Météorologie Dynamique) is working on improving spectroscopy data, end-to-end modelling of the instrument to study the sensitivity of measurements to different sources of uncertainty, developing an inversion system to study the impact of certain data processing parameters, setting up measurement campaigns to better understand methane variability and fluxes, as well as developing a ground-based differential absorption lidar for CH4 profiling.

A new Differential Absorption Lidar (DIAL) for atmospheric methane (CH4) profile measurement is under development at LMD. The lidar emitter is a new hybrid fibered/bulk Er:YAG laser. Two Erbium doped fiber lasers at 1532 nm are used to pump an Er:YAG rod in a ring cavity. The pulsed laser is sequentially injection-seeded by 2 fiber coupled CW Distributed Feedback (DFB) laser diodes On and Off respectively in the center of the methane line triplet at 1645.55 nm and out of at 1645.3 nm. It delivers dual On/Off 8 mJ/ 300 ns pulses at a repetition frequency of 1 kHz but other configuration can also be chosen. In this paper, we will present the objectives of this work, describe the experimental set-up and the laser performances with respect to power efficiency, beam quality, spectral purity and stability.

Our understanding of the global carbon cycle needs for new observations of CO2 concentration at different space and time scales but also would benefit from observations of additional tracers of intra-atmospheric or surface-atmosphere exchanges to characterize sources and sinks. Lidar is a well-known promising technology for this research as it can provide, at the same time, structure of the atmosphere, dynamics and composition of several trace gas concentration. In this framework, a coherent differential absorption lidar (CDIAL) has been developed at LMD to measure simultaneously and separately 12CO2 and 13CO2 isotopic composition of CO2in the atmosphere. It also provides the wind speed along the line of sight of the laser with an additional Doppler ability. This paper investigates the methodology of three wavelengths DIAL in the spectral domain of 2-µm to obtain range-resolved CO2 isotopic ratio d13C. The set-up of the lidar as well as the signal processing is described in details. First atmospheric measurements along three days are achieved in the surface layer above the suburban area of Ecole Polytechnique campus, Palaiseau, France. Typical performances of the instrument (median values along 70h of measurement) with 10 min of time averaging show: (1) a precision around 0.6% for 1.2 km range resolution for 12CO2 mixing ratio (2) a precision around 3.2% for 1.6 km range resolution for 13CO2 mixing ratio. In situ co-located gas analyser measurements are used to correct for biases that are explained neither by the spectroscopic database accuracy nor the signal processing and will need further investigation. Nevertheless, this preliminary study enables to make a useful state of the art for current lidar ability to provide d13C measurements in the atmosphere with respect to geophysical expected anomalies and to predict the necessary performances of a future optimized instrument.

Methane (CH4) is the second anthropogenic greenhouse gas (GHG) in the atmosphere that contributes to the global warming after CO2. If the methane emissions have a unique sink by OH oxidation, the various different sources, both anthropogenic (around 2/3) and natural, make complex the understanding of its atmospheric concentration. On the anthropogenic side (mainly gas exploitation and burning) it is fundamental to have a tool to verify inventories at different scales (from local methanizer to megacity) and prevent production network leakage in the atmosphere. As for surface-atmosphere exchanges of CO2, it is fundamental to study at different scales the spatial pattern and magnitude of the natural CH4 sources (biogenic anaerobic degradation of organic matter in wetlands, landfill and waste, livestock, rice cultivation, thermite, geological sources) and to understand their evolution with the global warming.Lidar has an important role to play in such topic as it can make: (i) a 3D mapping of CH4 concentration in anthropogenic plumes, (ii) vertical profiles to study transport processes in the atmosphere, (iii) even measure direct flux and (iv) provide CH4 Earth global measurements from a space platform as it will be for MERLIN CH4 integrated path differential absorption lidar CNES/DLR ongoing mission.A new ground-based Differential Absorption Lidar (DIAL) for atmospheric methane (CH4) profiling has been developed at LMD. The lidar emitter relies on a new hybrid fibered/bulk Er:YAG laser that delivers dual On/Off 8 mJ/ 300 ns pulses at a repetition frequency of 1 kHz in the methane line triplet at 1645.55 nm and out of at 1645.3 nm. It is associated with a direct detection receiver with a 50cm diameter telescope, a 2-nm linewidth interference optical filter, a near infrared photomultiplier (PMT) and a data acquisition and real time signal processing system working both in analogic and photon counting mode depending the application. First horizontal and vertical measurements in the atmosphere have been achieved and compared with in situ sensor and will be presented at the conference.

One of the greatest challenges facing environmental science is to better understand the impacts of predicted future changes in the terrestrial hydrological cycle. It has been recognized that human activities play a key role and must therefore be considered in future climate simulations. The representation of anthropization in land surface schemes within global earth system models is at a relatively nascent stage and must be improved for more accurate future projections of water resources. The understanding of the impact of anthropogenic processes has been hampered by the lack of consistent and extensive observations. Here, we present the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) project field campaign which brought together ground-based (surface energy budget estimated at 7 sites, 269 radio soundings made at 2 sites and multiple remote sensing instruments for profiling the lower atmosphere), airborne measurements (3 airplanes and numerous drones measuring surface and atmospheric properties) and satellite data (to derive estimates of irrigation timing, soil moisture, evapotranspiration and surface temperature) to improve our understanding of key natural and anthropogenic land processes and boundary layer feedbacks. The study area is in the Ebro basin of northeastern Spain in a hot, dry Mediterranean climate, with a sharp demarcation between a vast intensively irrigated region and a much drier rainfed zone to the east. Analysis of the observations reveal strong surface heterogeneities of evapotranspiration within the irrigated zone (differences upwards of approximately 7 mm day-1 between fields), linked to the crop type, vegetation phenology and soil moisture, all of which were modulated by irrigation. The significant surface flux differences between the irrigated and rainfed zones were found to result in strongly contrasting atmospheric boundary layer properties (between 2 supersites​ separated by 14 km) extending upwards through the lowest several km of the atmosphere.

The link between scalar second-order moments and gradient in the interfacial layer (IL) capping the convective boundary layer (CBL) is analysed using new lidar turbulent-scale observations. Temperature and moisture variances as well as sensible and latent heat fluxes have been measured during 100 hours in CBL temperate and arid regions with various free-cloud meteorological conditions. The IL fluxes and variances have been confronted with Lagrangian Stochastic Model (LSM) theories using scalar gradients, vertical velocity variance, kinetic energy dissipation rate and integral scales of turbulence with the purpose to build a local parametrization. The results show that a Pearson diffusion model in a stratified flow, that relies on the IL vertical velocity variance, and buoyant oscillation period, and 1 as the critical scale of turbulent diffusion, gives universal relevant parameters for IL temperature and moisture flux and variance. Our observations enable to infer for the first time IL local scaling for temperature, and moisture eddy diffusivities. The LSM local scaling parameters have been compared successfully for temperature with previous large-eddy simulations and with in-situ observations made in the nocturnal stratified atmospheric surface layer. Other LSM tested in this work that uses different scales to characterize IL scalar statistics, failed, especially for moisture statistics.

Fifteen transitions of the 20012-00001 band of 13CO2 in air have been recorded at 296 K using a cavity ring-down spectrometer linked to an optical frequency comb referenced to a GPS-disciplined Rb oscillator. In parallel, measurements of 12CO2 in air were made with a Fourier transform spectrometer for transitions belonging to the same 20012-00001 band, enabling comparison of the air-induced half-width and line shift coefficients of both isotopologues. For that, a multi-spectrum fit procedure is adopted with a Hartmann-Tran (HT) line profile. A decrease of about 0.4% is demonstrated for the 13CO2 air-broadening coefficients compared to the corresponding values of the main isotopologue. To the best of our knowledge, this observation is the first experimental evidence of an isotopic effect on the air-broadening coefficients in CO2 (which are generally assumed to be independent of the isotopologue in spectroscopic databases). On the theoretical side, a refinement of the simple model described in [Lamouroux et al. JQSRT 111;2010:2321] is proposed which enables the determination of the air-broadening coefficients for the 13CO2 isotopologue from the 12CO2 values. In addition, complex Robert-Bonamy-Ma (CRBM) calculations have been performed for 12CO2 and 13CO2 in collision with N2 or O2 for the 20012-00001 band with J '' values from 0 to 85. From these CRBM data, the 13CO2-air and 12CO2-air half-width and line shift coefficients were computed and the obtained isotopologue effect on these parameters was compared to the experimental data. A good average agreement is achieved for the CRBM calculations for the air-broadening coefficients while the simple model leads to slightly smaller isotopic effects. In contrast, for the air-pressure shift coefficients, a quite large disagreement is observed between the calculations and the experimental data.

We present a hybrid fiber/bulk laser source designed for CO2 and wind monitoring using differential absorption LIDAR (DIAL) and coherent detection at 2.05 mu m. This source features a master oscillator power amplifier (MOPA) architecture made of four fiber stages and one single-pass, end-pumped, bulk amplifier. This Letter focuses on the single-pass bulk amplifier performance and on the hybrid architecture benefits for DIAL and coherent detection. The bulk material is a holmium-doped YLF crystal that provides high efficiency amplification at 2.05 mu m. This laser offers an energy breakthrough as compared to the classical stimulated Brillouin scattering (SBS) limit encountered in a fiber laser without compromising robustness, thanks to very few free-space optical elements and a small optical path. It delivers pulse energy and repetition frequency of 9.0 or 1.2 mJ/20 kHz with 200 ns quasi Fourier-transform limited pulses.

L’exploration de l’atmosphère par lidar a commencé il y a maintenant 40 ans au LMD. L’observation lidar à partir de l’espace comme frontière ultime a motivé le développement de briques technologiques et d’instruments innovants sol et aéroporté ainsi que le traitement de signal nécessaires pour obtenir des données 4-D de plus en plus précises et exactes sur l’atmosphère (les aérosols, les nuages, la température, la dynamique et la concentration des principaux gaz à effet de serre H2O, CO2 et CH4) et la surface (fluorescence et structure de la canopée). Le LMD a notamment participé à la construction des missions Lidar spatiales d’observation de la Terre Calipso (NASA-CNES), ADM-Aeolus (ESA), EarthCARE (ESA-JAXA) et MERLIN (CNES-DLR).

This publisher's note contains a correction to Opt. Lett.49, 969 (2024)10.1364/OL.510598.

We present a hybrid fiber/bulk laser source at 1.645 mu m designed for methane (CH4) monitoring using differential absorption lidar (DIAL) measurements in the atmosphere. The emitter is also suited for coherent wind Doppler lidar. It relies on a Q-switched Er:YAG ring cavity pumped by erbium fiber lasers at 1532 nm. The pulsed laser is sequentially seeded by two fiber-coupled CW distributed feedback (DFB) laser diodes in the center of the CH4 line multiplet at 1645.55 nm (ON wavelength) and out of at 1645.30 nm (OFF wavelength). Despite a gain difference in the crystal between the ON and OFF wavelengths, pulses with equal energies and durations (9 mJ/300 ns) are obtained at a rate of 1 kHz. The spectral stability and purity properties in the dual-wavelength operating regime are presented. (c) 2024 Optica Publishing Group. All rights, including for text and data mining are reserved.

Model parametrizations in the convective boundary layer are still at work especially in the interfacial layers with the surface and the free troposphere. The present paper reports simultaneous turbulence-scale lidar observations of wind speed, temperature and specific humidity in the convective boundary layer in temperate and semi-arid regions. The collected data are used to assess new parametrizations in particular in the entrainment layer.

A ground-based mobile 3D lidar observatory has been developed for simultaneous measurements of wind speed, temperature, water vapor and carbon dioxide absorption in the atmosphere. The present paper reports details of the instruments, assesses the current performances and gives some examples of measurements for different geophysical applications.